The Grit question?

I have a trio of OEGB chicks ( 7 weeks old ) and I wonder if they are old enough to have grit and greens in their diet? These are my first chickens since 1958. They have grow crumbles always in the pen with them but when I take them out in the yard ( daily ) they peck and pull leaves off the pole beans and tomato plants and seem to enjoy the leaves a lot.
Also the roo managed to catch a grasshopper when it blundered in the cage.
My problem is the local feed store only has grit in 50 lb bags and the chicks only will be in the cage about 2 weeks till I get the coop & run finished and predator proof.
Can I go to the river and scoop up river sand & gravel and put in the pen in a cake pan for them? What size gravel/sand do they need ? I am guessing we are not talking pea gravel or larger?

They are still very small at that age so coarse sand would suffice. Yes, any source is fine. I get my grit pre-winter from the driveway. Of course I'm grabbing small pebbles at that age.

Once they are in a pen they'll be digging about the ground and finding grit on their own. I don't give chicks anything excepting starter feed until they are outside then let them scratch about and get their own grit to aid in the forage feed they are then getting. They only reason I grab a small pail of grit pre winter is the ground here is frozen solid.

The real gig on grit is that it aids in breaking down foods to get more of the nutrients out of it. Without grit they will consume more feed. So purchasing crushed granite to me just doesn't make a lot of economic sense unless your raising birds that never see earth and need to save on pellet feed consumption. In winter I toss a handful or two on the ground every two weeks.

They are still very small at that age so coarse sand would suffice. Yes, any source is fine. I get my grit pre-winter from the driveway. Of course I'm grabbing small pebbles at that age.

Once they are in a pen they'll be digging about the ground and finding grit on their own. I don't give chicks anything excepting starter feed until they are outside then let them scratch about and get their own grit to aid in the forage feed they are then getting. They only reason I grab a small pail of grit pre winter is the ground here is frozen solid.

The real gig on grit is that it aids in breaking down foods to get more of the nutrients out of it. Without grit they will consume more feed. So purchasing crushed granite to me just doesn't make a lot of economic sense unless your raising birds that never see earth and need to save on pellet feed consumption. In winter I toss a handful or two on the ground every two weeks.